1. Field of the Invention
The present invention relates to a thin film magnetic head array and more particularly to magnetic heads which are closely packed in a linear array for multiplexing data to achieve high data rates.
2. Description of the Related Art
Some read and or write applications require a high data rate (Gb/s). An example is high definition television (HDTV) which requires a data rate of approximately 1.2 Gb/s. Magnetic tape used for HDTV may include a number of tracks varying from 4 to 32. Another example of a read/write application which requires a high data rate is a data library which stores large volumes of data on magnetic disks. The only practical way to handle high data rates is to multiplex the data onto a plurality of tracks using a thin film magnetic head linear array. All of the magnetic heads in the array will either write simultaneously or read simultaneously to achieve the multiplexing of data. The multiplexed data can be transduced with either magnetic tape or magnetic disk media.
High data rates cannot be effectively achieved without using thin film technology to construct magnetic transducing heads. Thin film technology allows magnetic heads to be small, effective and cheap to manufacture using batch techniques. The problem is that present day thin film magnetic heads have a large footprint with significant lateral spacing which increases track pitch, thereby reducing the number of tracks which can be written per unit of medium area. Another problem with prior art thin film magnetic heads is that when they are arranged in a linear array, their off-track performance is very poor. The off-track performance problem is much more serious with a linear array of magnetic heads than it is with a single magnetic head. This is because of the long dimension of the array. A slight change in temperature will cause an unacceptable movement of the magnetic heads relative to the tracks which results in unacceptable sidewriting or sidereading. This is known as thermal induced track misregistration (TMR). To correct this problem the magnetic media must have guard bands between the data tracks which limits the track density.
The typical read/write inductive thin film magnetic head has a "pancake" type structure. The pancake type head has top and bottom pole layers. Between the pole layers is a multi-turn spiral coil layer and several insulation layers. The top and bottom pole layers terminate in pole tips which are separated by a gap layer. Because of the lateral dimension of the coil layer, the pancake type head has a footprint which is at least 300 .mu.m wide. When only one thin film magnetic head is employed, the track width can be in the order of 3 .mu.m. This is because with today's technology the pole tips can be defined with narrow widths. However, when a number of pancake heads are arranged in a side-by-side relationship to form a linear array, the track pitch takes on the lateral spacing between the thin film magnetic heads. Typically, the head-to-head spacing in pancake head arrays is on the order of 300 .mu.m. This means that track pitch on the magnetic media must likewise be about 300 .mu.m when pancake heads are employed in a magnetic head linear array. Such a pitch is unacceptable.
J. M. Coutillier, et al. in an article entitled "A 384 Track Fixed Recording Head" published in Digest of Intermag 1992, paper DP-09, show using an N.times.M matrix of heads on a single substrate. The heads are constructed to provide narrow track widths, while the rows are alternately offset to reduce track pitch. Nonetheless, the track pitch is still 216 .mu.m. It is desirable for present day applications that track pitch be much less than 216 .mu.m.